United States Patent Office Patented July 1, 1969
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3,453,337 United States Patent Office Patented July 1, 1969 1. 2 3,453,337 FLUORINATION OF HALOGENATED The presence in the reaction mixture of the two fluo ORGANIC COMPOUNDS rides, or the complex fluoride enables better yields of Royston Henry Bennett and David Walter Cottrell, Ayon highly fluorinated products to be obtained under less mouth, England, assignors to Imperial Smelting Cor severe reaction condions, markedly increases the amount poration (N.S.C.) Limited, London, England, a British of fluorination reagent reacted under otherwise similar company conditions and enables the fluorination reaction to be No brawing. Filed Feb. 19, 1965, Ser. No. 434,128 carried out (for the same yield of product) at a lower Claims priority, application Great Britain, Feb. 26, 1964, temperature with the consequent use of less costly ma 7,932/64 terials and techniques of reactor construction. The pres Int, C. C07c 25/04 10 ence of the fluorides enables the vapor phase reaction U.S. C. 260-650 2 Claims to be carried out (for the same yields) at lower pressure This invention relates to the fluorination of organic than the pressure involved in the reactions using only halogen compounds and more especially to a process the alkali metal fluorides as proposed hitherto. The fur for the production of highly fluorinated aromatic com ther possibility of using a continuous flow apparatus such pounds by the replacement of higher halogen atoms in 15 as a fluidised reactor will be apparent to those familiar halogeno-aromatic compounds by fluorine atoms. with the art. The presence of the two fluorides or com Aromatic halogenocarbons containing carbon and halo plex fluoride enables a lower temperature to be em gen atoms only can be reacted with alkali fluorides ployed than was hitherto believed to be necessary, with under various conditions to give yields of halofluoro a consequent reduction in the extent of thermal degrada aromatic compounds. However, where high yields of 20 tion. Low thermal degradation is a considerable advantage highly fluorinated aromatic compounds are required, this in that the reduction in the amount of tar-like degrada process suffers from disadvantages in that drastic reaction tion product facilitates the regeneration of the inorganic conditions and expensive fluorinating reagents are neces residues containing metal chloride plus unreacted metal sary. For example, in the reaction of hexachlorobenzene fluoride, into metal fluoride. This regeneration of the with alkali metal fluorides to give hexafluorobenzene, the 25 alkali metal fluoride is readily achieved by the use of better yields of hexafluorobenzene are only obtainable by hydrogen fluoride as a source of fluorine. Thus, the proc the use of the more expensive inorganic fluorides, e.g. ess including the regeneration is a further feature of caesium fluoride or by high temperature conditions cou the invention. pled with long reaction times using potassium fluoride. It will be a convenient aid to understanding this in The rates of the reactions concerned appear to limit the 30 vention if previous work of the same applicant is con yields of highly fluorinated aromatic compounds ob sidered. tainable under milder conditions and for shorter reaction This earlier work consisted of a process for the pro times. duction of aromatic perhalogenocarbons containing fluo We have now discovered that if the fluorinating agent rine atoms attached to the aromatic nucleus in which is modified by the inclusion of a fluoride chosen from 35 an aromatic compound containing carbon and halogen the group comprising fluorides of elements having a atoms only including at least one halogen atom other valency of between 2 and 6 inclusive, such fluorides being than fluorine is heated with at least one dry monovalent derived from the stable valency states of the elements metal fluoride in the absence of solvents and at a tem concerned, then enhanced yields of highly fluorinated aro perature between 300 and 750° C. matic compounds can be achieved using much milder 40 The metal fluoride used was preferably pelleted, or reaction conditions and shorter reaction times. used in the form of a powder. The reactions could be The invention consists in a process for fluorination of carried out at Sub-atmospheric, atmospheric or super organic halogen compounds in which (a) a mono-valent atmospheric pressures but pressures in the range of 10 to ionic fluoride, such as an alkali metal fluoride, together 50 atmospheres are preferred. Flow systems might be with (b) one or more fluorides of elements having a 45 used but sealed pressure vessels, e.g. autoclaves, were the valency from 2 to 6, present in their stable valency states preferred apparatuses for carrying out this process. are contacted with the organic halogen compounds pref Within the broad scope of that invention there were erably in a vapour phase reaction. preferred conditions for certain types of starting material. The invention further consists in a process for the In one particularly valuable form of the earlier pro production of highly fluorinated aromatic compounds 50 posals the aromatic compound used was a perhalocom in which an aromatic compound containing carbon and pound of formula CsClsF6 where n is an integer from halogen atoms only is contacted with a mixture of in 1 to 6 inclusive. In this case the metal fluoride is pref organic fluorides comprising (a) a monovalent ionic erably caesium, rubidium or potassium fluoride or their fluoride and (b) one or more fluorides of elements hav mixtures, and the temperature may lie between 350° C. ing a valency from 2 to 6, present in their stable valency 55 states (so that the said fluorides have no oxidising prop and 650° C. However, other sub-groups of fluorides and erties when used in accordance with the invention). preferred temperature ranges were shown to be valuable. The monovalent ionic fluoride may be an alkali metal (a) in which in was an integer from 3 to 6 inclusive; the fluoride such as LiF, NaF, RbF, CSF, etc. The other metal fluoride used was potassium fluoride; and the fluoride may conveniently be added to the reaction mix 60 temperature was between 400° C. and 600 C. ture in the form of the alkali metal salts of the corre (b) in which in was 1 or 2; the metal fluoride was potas sponding fluoro-anions. Thus, for example, BFs may be sium fluoride; and the temperature was between 400 added as KBF SnF, may be added as KSnF6. Other -C. and 600° C. complex salts which may be used according to the in (c) in which the metal fluoride used was potassium fluo vention are NaBFA, KPF6, KTiF6 or KSiF6. 65 ride; the temperature was between 500 C. and 600 3,453,337 3 4 C.; and the pressure was between 20 and 50 atmos- Examples 1 to 4 pheres. 8.0 g. hexachlorobenzene were heated for 10 hours at (d) in which in was between 2 and 6 and the metal fluo ride used was sodium fluoride. 500 C. with (1) potassium fluoride, (2) potassium fluo (e) in which in was between 2 and 6; the metal fluoride borate, (3) and (4), a mixture of potassium fluoride with used was sodium fluoride; and the temperature was be- 5 potassium fluoborate. The results show that the mixture tween 450° C. and 600° C.; preferably the pressure of the two salts gave a significantly greater yield of hexa was between 20 and 50 atmospheres. fluorobenzene than either salt alone. CsCls, g. KF, g. KBF4, g. CsIF6, g. CoClFs, g. CsCl2F1, g. CsCl3F3, g. CsClF2, g. CeCls F, g. CoCl6, g. 8.0 12.7 0. 0.66 1.9 2.0 1.0 0.04 O 0. 3.0 0. 7.7 O 0 0 0 0.02 0.24 1. 8.0 12.2 0.25 1.5 1.7 ... 4 0.7 0.04 O () 8.0 12.3 2.5 2.5 1.4 0.4 0.25 0.07 O O (f) in which in was between 4 and 6; the metal fluoride Examples 5 and 6 used was lithium fluoride; and the temperature was be tween 450 C, and 600 C. 20 8.0 g. hexachlorobenzene were heated for 10 hours at In another form of the earlier invention the aromatic 500 C. with sodium fluoride (Example 5) and a mixture compound was a perhalogenobenzene of formula CBrF6 where n is from 1 to 6 inclusive, and the tem- of sodium fluoride with sodium fluoborate (Example 6). perature was between 350° C. and 550° C. The results show a greater extent of fluorination in the In yet another form of the earlier invention the aro- 25 presence of the mixture. No. CoCls, g. NaF, g. NaBF4, g. CF, g. CsClFs, g. CsCl2F, g. CsCl3F, g. CsClF2, g. Co.ClsF, g. C6Cls, g 9---------- 8.0 9.0 O 0. 0. 0.06 0.9 2.5 2.2 0.5 6---------- 8.0 9.0 1.2 0 0.02 0.4 , 8 2.5 ... 5 0.3 matic compound used was a perhalogenonaphthalene of 35 Examples 7 to 12 formula F,e? sois betweeng and 1s and C.8 andErio the tem-in 8.0 g. of hexachlorobenzene were heated withd approxi this case the alkali metal fluoride used was caesium, mately 12 g. of potassium fluoride at 500 for 10 hours. rubidium, potassium or sodium fluoride or mixtures there- The addition to the reaction mixture of the compounds of and the temperature is between 400° C. and 500° C. 40 named in column 4 causes significantly increased extents In another useful sub-division of the process the alkali of fluorination: No.